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Enhancer remodeling by OTX2 directs specification and patterning of mammalian definitive endoderm.

The molecular mechanisms that drive essential patterning events in the mammalian embryo remain poorly understood. Analysis of transcription factor expression kinetics at peri-gastrulation stages of development suggest Otx2 as a candidate regulator of the definitive endoderm, the precursor of all gut-derived organs. Accordingly, timed OTX2 depletion in gastruloids or during directed differentiation results in abnormal definitive endoderm specification in mouse and human, characterized by altered expression of components and transcriptional targets of the canonical WNT signaling pathway, perturbed adhesion and migration programs, and de-repression of regulators of other lineages. These defects cumulate in impaired foregut formation. Mechanistically, OTX2 is required to activate a subset of endoderm-specific enhancers and to suppress select enhancers of other lineages, allowing timely exit from the primitive streak and correct specification of anterior endoderm. Our results establish OTX2 as an early gut regulator and suggest molecular principles underlying spatiotemporal cell identity conserved across germ layers and species.

Otx Transcription Factors

The scramblases VMP1 and TMEM41B are required for primitive endoderm specification by targeting WNT signaling.

The ER-resident proteins VMP1 and TMEM41B share a conserved DedA domain, which confers lipid scramblase activity. Loss of either gene results in embryonic lethality in mice and defects in autophagy and lipid droplet metabolism. To investigate their role in pluripotency and lineage specification, we generated Vmp1 and Tmem41b mutations in mouse embryonic stem cells (ESCs). We observed that ESCs carrying mutations in Vmp1 and Tmem41b show robust self-renewal and an unperturbed pluripotent expression profile but accumulate LC3-positive autophagosomes and lipid droplets consistent with defects in autophagy and lipid metabolism. ESCs carrying combined mutations in Vmp1 and Tmem41b can differentiate into a wide range of embryonic cell types. However, differentiation into primitive endoderm-like cells in culture is impaired, and the establishment of extra-embryonic endoderm stem (XEN) cells is delayed. Mechanistically, we show the deregulation of genes that are associated with WNT signaling. This is further confirmed by cell surface proteome profiling, which identified a significant reduction of the WNT-receptor FZD2 at the plasma membrane in Vmp1 and Tmem41b double mutant ESCs. Importantly, we show that transgenic expression of Fzd2 rescues XEN differentiation. Our findings identify the role of the lipid scramblases VMP1 and TMEM41B in WNT signaling during extra-embryonic endoderm development and characterize their distinct and overlapping functions.

Animals

Gata3 dosage governs primitive endoderm versus trophectoderm specification in embryonic stem cells.

Transcription factor (TF) dosage represents an overlooked aspect of developmental regulation. While Gata3 has traditionally been viewed as a determinant of trophectoderm (TE), its potential role in primitive endoderm (PE) has remained unclear. Here, we demonstrate that Gata3 functions as a dosage-sensitive regulator directing mutually exclusive lineage programs in mouse embryonic stem (ES) cells. Low levels of Gata3 (Gata3-L) promote PE-like transcriptional states, while high levels (Gata3-H) drive TE identity by rapidly repressing pluripotency and inducing TE markers. Genome-wide binding analysis reveals a dose-dependent redistribution of Gata3 across enhancers, with chromatin engagement consistent with pioneer factor-like activity. Functional 3D blastoid assays combined with single-cell transcriptomics further establish that Gata3 dosage alone is sufficient to instruct the spatial segregation of PE- versus TE-like compartments. These findings redefine Gata3 not merely as a TE determinant but as a central dosage-sensitive switch in lineage specification. More broadly, our results position TF dosage as a fundamental regulatory parameter that integrates enhancer selection, chromatin engagement, and spatial patterning, providing new opportunities to refine stem cell-based models and engineer developmental outcomes.

GATA3 Transcription Factor

Endodermal Organoids Along Two Axes: Single-Organ Fidelity, Inter-Organ Reconstruction, and the Unbuilt Gut-Lung Frontier.

Three-dimensional organoids of the gut, liver, and lung have become mainstream models of human development, disease, and therapy. These organs share an embryonic endodermal origin, yet the field measures their progress inconsistently because the word "maturity" carries two unrelated meanings. Herein, we review the organoid work across all three organs and propose that the two orthogonal axes of advancement be analyzed separately. The first axis is single-organ fidelity. Adult stem cell organoids are faithful but partial, reproducing the adult epithelium of their source tissue with genomic stability yet lacking stromal, vascular, immune, and neural compartments. Human pluripotent stem cell organoids are complete but immature, co-emerging with multiple lineages yet arrested in a fetal-like state. The cost of each limitation is organ-dependent, smallest in the intestine, largest for hepatic drug metabolism, and most spatially defined across the proximal and distal lungs. The second axis is inter-organ reconstruction, where progress is strongly asymmetric. The gut-liver axis is comparatively advanced and sustained by linked organoid and microphysiological systems. The gut-lung axis, by contrast, remains the least-developed frontier, and no such linked organoid has yet been built. We therefore frame it as a proposal, using in vivo and correlative evidence to outline the design principles for such a model. Four bottlenecks recur across both axes: limited vascularization; batch-to-batch variability; organ-skewed immune, microbial, and stromal microenvironments; and unidirectional signaling. We argue that benchmarking models against single-cell developmental atlases and prioritizing construction of the gut-lung frontier should guide the field over the next decade.

Intestines

Foxh1 is a locus-specific PRC2 recruiter governing germ layer silencing.

Polycomb Repressive Complex 2 (PRC2) establishes H3K27me3 marks to shape spatiotemporal gene expression during embryogenesis. While its dysregulation is linked to developmental disorders, cancer, and aging, the mechanisms guiding PRC2 to specific genomic loci remain a subject of ongoing debate. A prevailing model proposes that PRC2 recruitment occurs via its intrinsic affinity for chromatin rather than through sequence-specific transcription factors. Here, we provide evidence that the maternally deposited pioneer transcription factor Foxh1 plays a critical role in directing PRC2 to specific genomic loci during zygotic genome activation in Xenopus. Foxh1 is a critical transcription factor mediating Nodal signaling, but it also plays an earlier role by pre-binding enhancers prior to signaling activation. This pre-binding is essential for forming enhanceosome complexes that trigger mesendodermal gene expression and drive gastrulation, in cooperation with other maternal transcription factors. Using maternal Foxh1-null embryos, we demonstrate that Foxh1 directly recruits Ezh2, the catalytic subunit of PRC2, to Foxh1-bound loci. Loss of Foxh1 impairs Ezh2 recruitment, leading to a global reduction in H3K27me3. These findings support a dual-function model in which Foxh1 not only activates endodermal gene expression in endoderm, but also recruits PRC2 to silence the same genes in ectoderm. This dual activity of Foxh1 allows the spatially coordinated epigenetic states of the endodermal gene regulatory program during early embryogenesis.

CRISPR/Cas9

Glycolytic activity instructs germ layer proportions through regulation of Nodal and Wnt signaling.

Metabolic pathways can influence cell fate decisions, yet their regulative role during embryonic development remains poorly understood. Here, we demonstrate an instructive role of glycolytic activity in regulating signaling pathways involved in mesoderm and endoderm specification. Using a mouse embryonic stem cell (mESC)-based in vitro model for gastrulation, we found that glycolysis inhibition increases ectodermal cell fates at the expense of mesodermal and endodermal lineages. We demonstrate that this relationship is dose dependent, enabling metabolic control of germ layer proportions through exogenous glucose levels. We further show that glycolysis acts as an upstream regulator of Nodal and Wnt signaling and that its influence on cell fate specification can be decoupled from its effects on growth. Finally, we confirm the generality of our findings using a human gastrulation model. Our work underscores the dependence of signaling pathways on metabolic conditions and provides mechanistic insight into the nutritional regulation of cell fate decision-making.

Glycolysis

Base editing reveals an essential role for NANOG in human embryogenesis.

Understanding how the first cell lineages in human development are specified and maintained has fundamental importance and clinical implications for regenerative medicine, infertility and pregnancy loss. Although mouse models have provided valuable insights into transcription factors regulating early development, translating these findings to human embryos has been limited by ethical, technical and biological constraints. Functional studies of transcription factors in human embryos have been hindered by nuclease-based genome editing approaches that induce genotoxicity1-3. Here, to overcome this, we applied ABE8e adenine base editing4,5 to precisely target an exon splice donor site, resulting in a splicing defect and functional knockout of the developmental regulator NANOG in human embryos. This approach did not trigger genotoxicity and showed limited off-target editing. Loss of NANOG disrupts pluripotent epiblast specification and instead cells differentiate towards a primitive endoderm (yolk sac) or trophectoderm (placental) transcriptional programme. Retention of primitive endoderm differentiation in NANOG-edited human embryos reveals a functional compensation that is distinct from mouse, underscoring the importance of directly investigating human development. Our findings demonstrate an essential role for NANOG in human pluripotency and epiblast specification and highlight the utility of base editing for functional interrogation of human development.

Journal Article

IRAK4 constrains cellular plasticity during chemically-induced cell fate reprogramming into multiple lineages.

Chemical reprogramming holds transformative potential for regenerative medicine. However, the regulatory mechanisms governing cell fate transitions are not well understood. Here, we identify Interleukin-1 Receptor-Associated Kinase 4 (IRAK4) as a barrier to multi-lineage reprogramming. Pharmacological inhibition of IRAK4 enhances the reprogramming of mouse embryonic fibroblasts (MEFs) through a chemically activated multi-lineage priming (CaMP) state and extraembryonic endoderm (XEN)-like intermediates, increasing colony formation, and the expression of core XEN regulators (Sox17, Gata4, Sall4, and Foxa2). Genetic knockdown of Irak4 similarly accelerates reprogramming, whereas its overexpression blocks cell fate transitions. IRAK4 inhibition enhances chromatin accessibility and reshapes cell cycle dynamics, characterized by G0/G1 shortening and G2/M lengthening, potentially contributing to multi-lineage state establishment. Furthermore, IRAK4 suppression enhances the direct conversion of MEFs to neuron-like and hepatocyte-like cells, which exhibit enhanced functional maturity, including increased glycogen storage and improved detoxification capacity. Our findings establish IRAK4 as a regulator that constrains cellular plasticity potentially by coordinating chromatin accessibility and cell cycle dynamics.

Animals

Med12 cooperates with multiple differentiation signals to facilitate efficient lineage transitions in embryonic stem cells.

Cell differentiation results from coordinated changes in gene transcription in response to combinations of signals. Fibroblast growth factor (FGF), Wnt and mammalian target of rapamycin (mTOR) signals regulate the differentiation of pluripotent mammalian cells towards embryonic and extraembryonic lineages, but how these signals cooperate with general transcriptional regulators is not fully resolved. Here, we report a genome-wide CRISPR screen that reveals both signaling components and general transcriptional regulators for differentiation-associated gene expression in mouse embryonic stem cells (mESCs). Focusing on the Mediator subunit-encoding Med12 gene as one of the strongest hits in the screen, we show that it regulates gene expression in parallel to FGF and mTOR signals. Loss of Med12 is compatible with differentiation along both the embryonic epiblast and the extraembryonic primitive endoderm lineage but impairs pluripotency gene expression and slows down transitions between pluripotency states. These findings suggest that Med12 helps pluripotent cells to efficiently execute transcriptional changes during differentiation, thereby modulating the effects of a broad range of signals.

Animals

Teratoma Formation and Genomic Profiling Using Multi-Omics Approaches.

Teratoma formation is the gold standard assay for evaluating the developmental pluripotency of human and mouse embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Following subcutaneous injection into immunodeficient mice, pluripotent stem cells spontaneously differentiate into derivatives representing all three embryonic germ layers-ectoderm, mesoderm, and endoderm. Beyond serving as a functional assay for pluripotency, teratomas provide a unique three-dimensional model system for studying early human development and lineage specification in vivo. This chapter describes comprehensive protocols for teratoma formation in immunodeficient mice, tissue processing for multiple downstream genomic applications, and multi-omics profiling approaches. We detail methods for embryonic stem cell culture, teratoma generation via subcutaneous injection, tissue dissection and processing for chromatin immunoprecipitation followed by sequencing (ChIP-Seq), RNA sequencing (RNA-Seq), single-cell multiome profiling combining chromatin accessibility (ATAC-Seq) and gene expression (scRNA-Seq), and histological analysis using hematoxylin and eosin (H&E) staining. Additionally, we provide bioinformatics workflows for analyzing the resulting genomic datasets to characterize the epigenetic and transcriptional landscapes of teratoma-derived tissues. These methods enable comprehensive molecular characterization of developmental processes and provide valuable resources for stem cell biologists studying pluripotency, differentiation, and early embryonic development.

Teratoma

Mouse totipotent blastomere-like cells model embryogenesis from zygotic genome activation to post implantation.

Embryo development begins with zygotic genome activation (ZGA), eventually generating blastocysts for implantation. However, in vitro systems modeling the pre-implantation development are still absent and challenging. Here, we used mouse totipotent blastomere-like cells (TBLCs) to develop spontaneous differentiation and blastoid formation systems, respectively. We found Wnt signaling enabled the rapid expansion of TBLCs and the optimization of their culture medium. We successfully developed a TBLC-spontaneous differentiation system in which mouse TBLCs (mTBLCs) firstly converted into two types of ZGA-like cells (ZLCs) distinguished by Zscan4 expression. Surprisingly, Zscan4-, but not Zscan4+, ZLCs further passed through intermediate 4-cell and then 8-cell/morula stages to produce epiblast, primitive endoderm, and trophectoderm lineages. Significantly, single TBLCs underwent expansion, compaction, and polarization to efficiently generate blastocyst-like structures and even post-implantation egg-cylinder-like structures. Conclusively, we established TBLC-based differentiation and embryo-like structure formation systems to model early embryonic development, offering criteria for evaluating and understanding totipotency.

Animals

Self-organization of sinusoidal vessels in pluripotent stem cell-derived human liver bud organoids.

The induction of tissue-specific vessels in in vitro living tissue systems remains challenging. Here, we directly differentiated human pluripotent stem cells into CD32b+ putative liver sinusoidal progenitors by dictating developmental pathways. By devising an inverted multilayered air-liquid interface culture, hepatic endoderm, septum mesenchyme, arterial and sinusoidal quadruple progenitors self-organize to generate and sustain hepatocyte-like cells neighboured by divergent endothelial subsets composed of CD32blowCD31high, LYVE1+STAB1+CD32bhighCD31lowTHBD-vWF- and LYVE1-THBD+vWF+ cells. WNT2 mediates sinusoidal-to-hepatic intercellular crosstalk potentiating hepatocyte differentiation and branched endothelial network formation. Intravital imaging reveals the iPS-cell-derived putative liver sinusoidal endothelial progenitor develops fully perfused human vessels with functional sinusoid-like features. Organoid-derived hepatocyte- and sinusoid-derived coagulation factors enable correction of in vitro clotting time with Factor V-, VIII-, IX- and XI-deficient plasma, and rescues the severe bleeding phenotype in haemophilia A mice on transplantation. Advanced organoid vascularization technology allows for interrogating key insights governing organ-specific vessel development, paving the way for coagulation disorder therapeutics.

Humans

Foxi2 and Sox3 are master regulators controlling ectoderm germ layer specification.

In vertebrates, germ layer specification represents a critical transition where pluripotent cells acquire lineage-specific identities. We identify the maternal transcription factors Foxi2 and Sox3 to be pivotal master regulators of ectodermal germ layer specification in Xenopus. Ectopic co-expression of Foxi2 and Sox3 in prospective endodermal tissue induces the expression of ectodermal markers while suppressing mesendodermal markers. Transcriptomics analyses reveal that Foxi2 and Sox3 jointly and independently regulate hundreds of ectodermal target genes. During early cleavage stages, Foxi2 and Sox3 pre-bind to key cis-regulatory modules (CRMs), marking sites that later recruit Ep300 and facilitate H3K27ac deposition, thereby shaping the epigenetic landscape of the ectodermal genome. These CRMs are highly enriched within ectoderm-specific super-enhancers (SEs). Our findings highlight the pivotal role of ectodermal SE-associated CRMs in precise and robust ectodermal gene activation, establishing Foxi2 and Sox3 as central architects of ectodermal lineage specification.

Ep300

Foxi2 and Sox3 are master transcription regulators that control ectoderm germ layer specification in Xenopus.

Germ layer specification represents a critical transition where pluripotent cells acquire lineage-specific identities. We identify the maternal transcription factors Foxi2 and Sox3 to be pivotal master regulators of ectodermal germ layer specification in Xenopus. Ectopic co-expression of Foxi2 and Sox3 in prospective endodermal tissue induces the expression of ectodermal markers while suppressing mesendodermal markers. Transcriptomic analyses reveal that Foxi2 and Sox3 jointly and independently regulate hundreds of ectodermal target genes. During early cleavage stages, Foxi2 and Sox3 pre-bind to key cis-regulatory modules (CRMs), marking sites that later recruit Ep300 and facilitate H3K27ac deposition, thereby shaping the epigenetic landscape of the ectodermal genome. These CRMs are highly enriched within ectoderm-specific super-enhancers (SEs). Our findings highlight the pivotal role of ectodermal SE-associated CRMs in precise and robust ectodermal gene activation, establishing Foxi2 and Sox3 as central architects of ectodermal lineage specification.

Animals